The present invention pertains to prosthetic heart valves and in particular to polymeric tri-leaflet heart valve prostheses.
Ever since 1950, when blood oxygenators made open heart surgery feasible, it has been possible to treat some forms of heart disease by replacing a patient""s heart valve with a prosthetic valve. A prosthetic heart valve is implanted into an annular opening in a heart created when the diseased valve is removed. Early heart valve prostheses included ball-and-cage valves and disc-and-cage valves in which a ball or a disc was housed in a cage. One side of the cage provided an orifice through which blood flowed either into or out of the heart, depending on the valve being replaced. When blood flowed in a forward direction, the energy of the blood flow forced the ball or disc to the back of the cage allowing blood to flow through the valve. When blood attempted to flow in a reverse direction, or xe2x80x9cregurgitate,xe2x80x9d the energy of the blood flow forced the ball or disc into the orifice in the valve and blocked the flow of blood.
A xe2x80x9cmechanicalxe2x80x9d valve is another type of prosthesis comprising an annular valve body in which one, two, or three occluders are pivotally mounted. The occluders are typically substantially rigid. The occluders move between a closed position, in which the occluders are mated and block blood flow in the reverse direction, and an open position, in which the occluders pivot away from each other and do not block blood flow in the forward direction. The energy of blood flow causes the occluders to move between their open and closed positions.
The valve leaflets of xe2x80x9ctissue valvesxe2x80x9d are usually flexible and made from tissue, such as specially treated porcine or bovine pericardial tissue. A tri-leaflet tissue valve comprises an annular valve body in which three flexible leaflets are mounted to a supporting portion of the valve body, called a xe2x80x9cstent,xe2x80x9d located at the circumference of the annulus. When blood flows in the forward direction, the energy of the blood flow deflects the three leaflets away from the center of the annulus and allows blood to flow through. When blood flows in the reverse direction, the three leaflets engage each other in a coaptive region, occlude the valve body annulus and prevent the flow of blood.
Heart valves made from a man-made material such as polyurethane or another biocompatible polymer may have two or three leaflets and may have a stent to increase the structural strength of the valve while allowing the leaflets to remain flexible. Polymeric valves may be sutured or pinned directly to the site of an explanted heart valve, or a sewing ring may be sutured to the valve body and sutures attaching the valve to the heart may pass through the sewing ring. In either case, suturing through a polymeric valve body is likely to alter or damage the polymeric material where a suturing needle is driven through the valve body. High stresses and stress concentrations at suture locations may damage the valve body material.
An important consideration in prosthetic heart valve design is the durability of the heart valve. One source of failure of polymeric heart valves is tearing of the polymeric material that forms the heart valve, for example, where a suture needle has been driven through elastic polymeric material.
The invention improves the durability of elastic polymeric heart valves by eliminating the need to pierce the elastic material of the heart valve during construction of the sewing ring or during implantation. The prosthetic heart valve comprises a stent with an annular base and a plurality of commissures rising from the base. A plurality of apertures or holes circumferentially spaced around the circumference of the base provide access points for a needle to draw a suture through the aperture. Flexible polymeric leaflets are cast or molded over the stent. Polymeric material forming the leaflets covers most of the stent, including at least part of the base. The polymeric material may surround the apertures or holes, leaving a central opening in each aperture through which the needle may be inserted without penetrating the polymeric material. Alternatively, only a portion of the base may be covered with polymeric material, such that the polymeric material does not extend to the apertures. In this configuration the needle can pass through an aperture without penetrating the polymeric material. The base may be flared outwardly, forming a frustro-conical ring, to facilitate formation of the central openings in each aperture when the polymeric material is molded over the stent.
A sewing ring may be mounted on the heart valve by suturing the sewing ring through the apertures in the stent. The sewing ring may be attached outside the base or inside of the base, if the base is flared outwardly.
The apertures or holes may have a variety of configurations, such as circular or elongated slots. The apertures may be formed as a plurality of notches along an edge of the base of the stent with a circumferential wire lying along the edge of the base and closing an open side of the notches.
Apertures may also be provided by extending an area covered by woven material around all or part of the circumference of the base.
It is an object, therefore, of the present invention to provide a polymeric prosthetic heart valve with means for attaching a sewing cuff or for suturing directly to the heart without puncturing a polymeric material.
It is another object of this invention to provide a polymeric prosthetic heart valve wherein the structural integrity of the valve material is not compromised by punctures during manufacture.
Yet another object of the invention is to provide a polymeric, stent-supported heart valve body having pre-formed apertures for attaching a sewing ring.
These and other objects and features of the invention will be apparent from the following detailed description, made with reference to the accompanying drawings.